Ion-exchange resins are used by industry to separate chemical species from solutions containing them. Such resins are prepared by substituting various functional groups onto a copolymer bead matrix. The functional groups are capable of associating with the impurities so as to remove them from solution. Ion-exchange resins may be cation-, anion-, or chelate-exchange resins, depending on the choice of functional group substituted onto the copolymer bead matrix. The copolymer bead matrix may also be used in preparing polymeric adsorbents, such as those disclosed in U.S. Pat. No. 4,950,332.
The copolymer bead matrix is typically prepared by suspension polymerization of a finely divided organic phase comprising monovinylidene monomers like styrene, polyvinylidene monomers such as divinylbenzene, a free-radical initiator, and, optionally diluents which are either phase-separating or soluble. The copolymer beads produced may be microporous, i.e., gellular in character, or macroporous, the result depending upon whether the phase-separating diluent is employed. The term "macroporous" as commonly used in the art means that the copolymer has both macropores and mesopores. The terms "microporous", "gel", and "macroporous" are well known in the art and generally describe the nature of the copolymer bead porosity. Microporous or gel copolymer beads have pore sizes on the order of less than about 20 Angstroms (.ANG.), while macroporous copolymer beads have both mesopores of from about 20 .ANG. to about 500 .ANG. and macropores of greater than about 500 .ANG.. Gel and macroporous copolymer beads, as well as their preparation, are further discussed in U.S. Pat. No. 4,256,840.
Recently, industry has focused on methods of preparing copolymer beads in multi-staged polymerizations, also known as seeded polymerization processes. Such copolymer beads are desirable due to good mechanical strength and osmotic shock resistance. Seeded polymerization processes can also prepare beads of relatively uniform size if the seed particles employed have similar size uniformity. U.S. Pat. Nos. 4,419,245 and 4,564,644 disclose processes wherein seed particles are suspended in a continuous medium and, thereafter, the seed particles are imbibed and polymerized with additional monomer to form copolymer beads. British Patent 1,151,480 discloses a process wherein copolymer beads are prepared from porous seed particles. European Patent Application No. 0 062 088 (Oct. 13, 1982) discloses preparation of gel or macroporous copolymer beads by a seeded polymerization process and European Patent Application No. 0 168 622 (Jan. 22, 1986) concerns preparation of macroporous copolymer beads by a seeded polymerization process using macroporous seed particles.
Crosslinked copolymers for ion exchange and absorbent resins are conventionally prepared by suspension polymerization with one to three isothermal stages wherein the heat generated by the polymerization exotherm is removed to maintain the isothermal conditions. The prior art conventional technology requires a long cycle time of 10-20 hours per batch and generates high polymer waste, especially with low crosslink recipes. In addition, reactors require excess heat removal capacity to maintain the isothermal conditions.
U.S. Pat. No. 4,239,669 teaches the emulsion polymerization of vinyl aromatic monomer and conjugated diene under adiabatic conditions in a continuous flow agitated reactor. The phase ratio is held low to hold the temperature to 80.degree.-100.degree. C. The emulsion particle size is 1000-1500 angstroms. This patent does not refer to the preparation of a suspension bead product and the particles produced are not hard crosslinked bead polymer used in the production of ion exchange resins.